Backup not completing/Progress window not closingIf you have just upgraded a FEBE major version (e.g., v7.x to v8.x), it is important that you clear FEBE preferences before attempting a backup (this step should also be done whenever the backup is not completing):

Go to Tools > FEBE > FEBE Options > Advanced > click "Clear FEBE preferences". This will remove all older version preferences and set the current preferences (options) to a default value. Firefox will automatically restart after clearing the preferences. You will need to specify a backup destination directory ('Where to backup' pane) and select backup type and options ('What to backup' pane) before attempting a backup.

Checking for FEBE errorsIf the progress meter in the FEBE progress window is not moving or the percentage count is not incrementing when a backup is performing, an error has most likely occurred.

Open and clear the Browser (error) console (Tools > Web Developer > Browser ConsoleorCTRL-Shift-J. Make sure at least the JS button is on (should have a non-white background - usually light blue)) . Minimize the error console and perform a backup. After a few seconds (when the progress meter stops moving) examine the error console for any FEBE related error messages (type febe in the "Filter output" box in the upper right of the error console. Select all/copy/paste (ctrl-A, ctrl-C, ctrl-V) them in a new post.

Set the FEBE Options > Advanced > Miscellaneous > Advanced preferences > Chrome script timeout to 0 (zero). This essentially turns off the time limit. Perform a backup and note the number of seconds it takes to complete the backup. (If it takes more than five minutes or if the progress bar in the FEBE progress window stops moving again, abort the backup -- It's not working.) Set the Chrome script timeout to the number of seconds the backup took plus 10. For example, if the backup took 90 seconds, enter 100.